Knowing that speed and efficiency are just as important as the fit and overall function of triathlon shoes, Fi'zi:k developed its new K5 Donna Shoes to seamlessly blend these attributes into a single design. The uppers were made using Fi'zi:k's Microtex for the support structure and nylon mesh for the ventilation windows. Together, these materials keep your feet breathing and comfortable. And for the insole, Fi'zi:k included its own Superlight version. It's not custom moldable like the top shelf K1, but it does incorporate a thoughtful design that assures comfort by absorbing road vibration and supporting your arch system. Also, where the K1 features a multi layered carbon fiber outsole, the K5 makes use of a carbon reinforced nylon outsole. And while this keeps costs down, it doesn't inhibit either comfort or much in the power transfer department. In fact, the K5 retains a low stack height and a high level of rigidity. For fit, Fi'zi:k incorporated its effective dual strap closure system. This allows you to really dial in the volume of the shoe, whether for training or on the fly during a race. For your T1 transitions, the two strap closure system is a breeze. The large top strap opens away from the drivetrain to allow a quick and seamless securing of the shoe. As for the bottom strap, you'll find that this is used less for transitions and more left alone once you've established your desired volume and fit. However, the gripper tabs placement on the strap simplifies any adjustments that you might need to make from the saddle. Fi'zi:k also added an oversized heel loop to aid in the transition process. The Fi'zi:k K5 Donna Shoes Women's are available in whole and half sizes 37. 0 to 43. 0 and in the color Silverwhite.